1. Field of the Invention
The present invention broadly relates to a composition comprising dual wavelength image-forming particulates which may be used with a substrate. The present invention also broadly relates to a process for preparing these dual wavelength image-forming particulates. The present invention additionally broadly relates to substrates treated on one or both sides with this dual wavelength imaging particulate-containing composition. The present invention further broadly relates a process for treating one or more sides of a substrate with these dual wavelength image-forming particulates. The present invention further broadly relates to a method for imaging of a substrate using these dual wavelength image-forming particulates.
2. Related Art
Electrophotography provides a non-impact printing technology for today's reprographic industries. A representative electrophotographic printing or copying process normally creates images on a coated polymeric substrate in five steps. These steps include: (1) depositing a uniform electric charge onto a photoconductor drum; (2) creating an electrostatic latent image on the photoconductor by exposing the photoconductor to an oscillating narrow laser beam that is turned on and off digitally or a stationary array of LED lights which are turned on and off digitally; (3) exposing the photoconductor to toner particles such that toner particles having the correct polarity adhere to the exposed latent image; (4) passing the medium to be printed between the photoconductor and a transfer corona to cause the toner particles to transfer from the photoconductor to the medium; and (5) fixing (e.g., fusing) the transferred toner particles on the medium.
For example, a form of electrophotographic printing is laser printing. In laser printing, there are essentially five steps. In the first step (charging), a primary charge roller projects an electrostatic charge onto the photoreceptor, a revolving photosensitive drum or belt, which is capable of holding an electrostatic charge on its surface as long as it hasn't been exposed to certain wavelengths of electromagnetic radiation. In the second step (writing), a raster image processor (RIP) chip converts incoming images to a raster image suitable for scanning onto the photoreceptor. A laser (or laser diode) is aimed at a moving mirror, which directs the laser beam through a system of lenses and mirrors onto the photoreceptor wherever the laser strikes the photoreceptor the charge is reversed, thus creating a latent electrophotographic image on the photoreceptor surface. In the third step (developing), the surface containing the latent image is exposed to toner, with the charged toner particles being electrostatically attracted to the photoreceptor where the laser wrote the latent image. In the fourth step (transferring), the photoreceptor is pressed or rolled over paper, thus transferring the image formed by the charged toner particles. In the fifth step (fusing), the paper with the transferred image passes through a fuser assembly having rollers that provide heat and pressure to bond or fuse the toner particles of the formed image to the paper.
Instead of electrophotographic printing such as laser printing, ink jet printers may be used. There are essentially three types of ink jet printers. The first category, thermal ink jet or bubble jet printers, work by having a print cartridge with a series of tiny electrically heated chambers constructed by photolithography. To produce an image, the printer runs a pulse of current through heating elements, causing steam in a chamber to form a bubble, which then propels a droplet of ink (usually water-based, pigment-based or dye-based) onto the paper. The ink's surface tension pulls another charge of ink into the chamber through a narrow channel attached to an ink reservoir.
A second category, piezoelectric ink jet printers, uses a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the crystal changes shape or size, which generates a pressure pulse in the fluid, thus forcing a droplet of ink from the nozzle. This is essentially the same mechanism as in the thermal inkjet printer but generates the pressure pulse using a different physical principle.
A third category, continuous ink jet printers, uses a high-pressure pump that directs liquid ink from a reservoir through a microscopic nozzle, thus creating a continuous stream of ink droplets. A piezoelectric crystal causes the stream of liquid to break into droplets at regular intervals, which are then subjected to an electrostatic field created by a charging electrode as they form. The field is varied according to the degree of drop deflection desired, thus resulting in a controlled, variable electrostatic charge on each droplet. The charged droplets are then directed (deflected) to the receptor material to be printed by electrostatic deflection plates, or are allowed to continue on undeflected to a collection gutter for reuse.
Technological advances in electrophotography and ink jet printers have brought an increase in the popularity of color electrophotographic printers and copiers, as well as color ink jet printer. Unlike a monochrome printer or copier wherein only a single toner or ink jet cartridge, i.e. black toner or ink jet cartridge, is employed, full color printing or copying may require as many as four toner or ink droplet cartridges which provide yellow, magenta, cyan, and black. Because a separate imaging process may be required for each of the four toner or ink printer cartridges, color printers and copiers may be much slower and more expensive than their monochrome counterparts. The recording media suitable for color printers and copiers may also need to meet more stringent requirements to provide a true full-color reproduction of the original.
Copying and printing using electrophotographic or ink jet processes does have some disadvantages, especially in terms of the toners and inks used to impart the resulting images. In electrographic copying or printing, the toner particles may not fuse properly, thus creating a messy product that can get on hands, clothes, etc. Depending on how much of the paper comprises the image, there may be some portion of the toner particles that are not adhered to the paper, but are instead collected as a residue that eventually may need to be disposed of. In ink jet printing, there are the conflicting requirements for a coloring agent that will stay on the surface, yet provide rapid dispersement of the carrier. Most ink jet printer cartridges use aqueous inks (e.g., based on a mixture of water, glycol and some dyes or pigments) that may be difficult to control on the surface of print media and therefore require may require specially coated media.
Accordingly, it would be desirable to develop a method of forming an image on a paper web or other substrate that provides for the high speed and high quality printed images without the deficiencies of ink jet and electrophotographic methods of printing.